1. Field of the Invention
The present invention relates to fire retardants for isocyanate-based foams. More particularly, the present invention concerns fire retardants for flexible or rigid isocyanate-based foams. Even more particularly, the present invention concerns fire retardants for flexible and/or rigid polyurethane foams.
2. Prior Art
The demand for very efficient additives to lower the combustibility of flame-retardant flexible urethane foams has strongly increased in recent years because of stricter fire regulations and the general, overall, need for safety. Thus, much effort has been devoted to providing flame retardant synthetic resinous products, as well as improved fire retardants, per se. This is especially true with respect to isocyanate-based foams, such as polyurethanes, polyisocyanurates and the like which are such an integral part of our every day surroundings. Thus, the art has produced many so-called "flame retardant" polyurethanes, polyisocyanurates, etc. Yet, upon close scrutiny, many of these so-called flame retardant foams have inherent drawbacks.
For example, so-called flame retardant flexible polyurethane foams have been prepared by the addition of halogen- and/or phosphorous-containing flame retardants. While these foams pass small scale fire tests, they do not reflect actual fire conditions. Therefore, the tests can be used only as laboratory scale methods for screening.
Further, the foams classified as self-extinguishing foams (SE foams) as determined by the ASTM D-1692-59T test are flammable under actual fire conditions.
Another proposed method of making flame retardant flexible foams is high resilience foams (HR foams) which have lower melting points than conventional flexible urethane foams. These foams are prepared by using a blended polyisocyanate, e.g., 80%/20% mixture of TDI and polymeric MDI. The low melting points of the foams result in a dripping phenomenon which prevents flame propagation. Accordingly, the foams also can be classified as SE foams by the ASTM D-1692-59T, but these foams also are substantially flammable at actual fire conditions.
Substantially non-combustible flexible foams can be produced only by the addition of extremely large amounts of power-type flame retardants, and not by liquid type flame retardants.
The first commercial product of this type is a CMHR foam (combustion modified high resilience foam) developed by Mobay Chemical Corp. (J. F. Szabat and J. A. Gaetano, Proceedings of the SPI International Technical/Marketing Conference, Nov. 2-5, 1983, San Diego, pp. 326-331). This type of foam employs alumina trihydrate as the major flame retardant.
Additionally, in recent years, many types of nitrogen-containing compounds have been proposed as powder-type flame retardants for flexible and rigid urethane foams. Melamine pyrophosphate has been used for rigid urethane foams, as disclosed in U.S. Pat. No. 4,003,861. Melamine-phenolphosphonic acid salt has been used for flexible foams, as described in U.S. Pat. No. 4,061,605.
Also, in U.S. Pat. No. 4,139,501 methylolmelamine alkyl ethers have been taught as flame retardants for flexible urethane foams. Melamine has been disclosed for rigid urethane foams in U.S. Pat. No. 4,221,875. Cyanuric acid derivatives, such as cyanamid, dicyandiamide, guanidine, biguanidine, and melamine have been disclosed as flame retardants for flexible urethane foams, as taught in U.S. Pat. No. 4,258,141.
Melamine-formaldehyde precondensates as flame retardants for flexible urethane foams are taught in U.S. Pat. No. 4,334,971. An intumescent composition, including melamine, for use in flexible urethane foams has been taught in U.S. Pat. No. 4,317,881, as well as urea or melamine as taught in U.S. Pat. No. 4,385,151. Other flame retardants are taught in U.S. Pat. No. 4,367,294; U.S. Pat. No. 4,369,268 and U.S. Pat. No. 4,454,254.
In contrast to the organic based flame retardants of the prior art, the present invention is based on the finding that ammonium sulfate is an unexpectedly effective flame retardant for active-hydrogen containing isocyanate-based foams.
Ammonium sulfate is an inexpensive chemical ordinarily used as a fertilizer. However, Applicant is unaware of any teaching of ammonium sulfate as a flame retardant for urethane foams and the like.